Conventionally, in the field of medical care, nursing care and the like, a distance monitoring system (i.e., remote monitoring system) for so-called nursing care, and the like, has been developed aiming at providing effective nursing with less staff by means of detecting movements of a patient, those cared for, and the like, in a hospital room wherein movement detection is conveyed to a nurse station or a ward through a cable or cable-free system. At the present time, the further development of this kind of a remote monitoring system is actively under way.
In recent years, monitoring systems employing an optical fiber as a monitoring sensor for monitoring living body activities have received widespread attention because of the excellent detection sensitivity and stability of the optical fiber. Specifically, while a conventional piezoelectric sensor or a vibration type sensor may be used to accurately detect, to some extent, human movements such as going to bed, rising from bed, or tossing and turning in bed, and the like, it is difficult to detect certain human movements, including respiration and pulse, with high accuracy by using a piezoelectric sensor or a vibration type sensor.
A monitoring system for detecting living body activities that employs an optical fiber is disclosed, for example, by Japanese Unexamined Patent Application No. 5-312966, by Japanese Unexamined Patent Application No. 8-584, and the like.
The aforementioned sensor technologies are all based on the fact that “when an optical fiber is abruptly bent, a linearity of light surpasses a light enclosure effect of light of the optical fiber core, thus bringing about the loss of a quantity of light due to the leakage of light”. However, there remain several disadvantages of these sensor technologies such as listed below in items a, b and c:
a. The optical fiber needs to be bent abruptly in order that a loss is brought about;
b. It is difficult to adjust the bending quantity due to the fact that loss increases exponentially to the bend radius. Thus, a specially designed tool is required to obtain an appropriate bend quantity;
c. There is a concern that the wire (optical fiber) may be broken or deteriorate due to fatigue when it is abruptly bent.
On the other hand, with optical fibers, it has been well known for a long time that the polarized wave conditions of the propagated light changes with changes of the shape of the optical fiber due to bending. Detecting systems for crime prevention have been developed based on this fact. For example, Japanese Unexamined Patent Application Publication No. 2000-40187, Japanese Unexamined Patent Application Publication No. 2001-6055 and the like, disclose an optical fiber fitted to a fence, and the like, in order to sense invaders and raise an alarm by means of detecting polarized wave fluctuations brought about by external forces applied to the optical fiber.
However, with Japanese Unexamined Patent Application Publication No. 2000-40187, and the like, the device disclosed is constituted so that the optical fiber is simply fitted to the fence for the purpose of sensing invaders approaching from outside. Therefore, it is difficult to immediately apply this technology for purposes of monitoring living body activities of a human being. In addition, because the device disclosed by Japanese Unexamined Patent Application Publication No. 2000-40187, and the like, is constituted so that external forces generated by an invader is directly applied to the optical fiber, and no consideration at all is made to enhance the sensitivity of detecting fluctuations of polarized wave conditions due to changes occurring when feeble pressure is applied, it would be difficult for a person of ordinary skill to immediately apply this sensing technology to a monitoring system for monitoring other human activities such as respiration and heart pulsation.
In addition, because polarized wave conditions of light traveling in an optical fiber are generally random, a so-called “polarized wave correction” is required in order to use the polarized wave as a sensor. However, the polarized wave correction is time-consuming to achieve, and then manufacturing costs go up because the apparatus for measuring polarized wave fluctuations is so complicated.
Applicants of the present invention have developed and disclosed a system with which a polarized wave quantity is detected in a simple manner and with high sensitivity in order to solve problems pertaining to detecting fluctuations of a polarized wave without requiring corrections of the polarized wave (Japanese Unexamined Patent Application Publication No. 2004-108918 and Japanese Unexamined Patent Application Publication No. 2004-184223). The present invention makes it possible to detect (or sense) all human activities and movements, including respiration and heart pulsation, with high accuracy by means of applying the system for detecting the quantity of polarized wave fluctuations to a system for monitoring activities and movements of a human.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 5-312966.    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 8-584.    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2000-40187.    [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2001-6055.    [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2004-108918.    [Patent Document 6] Japanese Unexamined Patent Application Publication No. 2004-184223.